Thread: Juroshek method for Equivalent SM of splitter

Hi,

Because we didn't get similar results from the results of two calibration of an 11667A power splitter equivalent source mismatch
I was trying to confirm that our labs method is correct by using a third method published in Oct 1997 by Juroshek which uses a SOLT calibration
of the VNA and splitter to obtain source match of the splitter used as an external port of the VNA.

An Agilent competitor in Germany has an application note which describes access to the source match term in service functions for specific analyzers.
Our cal lab E8361a opt 14 PNA seems to have the same receiver access and cal viewer allows user to see the residual terms so I wanted to try to duplicate this on the PNA.

I tried connecting the input (PS1) to PNA port 1; the left port PS2 (label up and PS1 away from me) to Port 2, and performed 10M-18GHz SOLT cal at
the third port of the splitter(PS3) using preset parameters using 85054B cal kit. The cal viewer source match term displayed a 12 db loss or about 1.6 VSWR.
I took this as the output S22 not the equivalent output source match, and not what I was after.

Then I removed the reference receiver jumper, terminated the source and took the PS2 port to the Port 1 reference receiver input.
The results of one and two port calibrations with unk thru were very similar.

Guidance on what I'm doing wrong would be appreciated as this seems to be an established method. Our lab implementation is terminated PS1 with PS2 and PS3
measured reflection and transmission on Port 1 and 2 then doing math. Those are the results I'm trying to validate. The other results are from Roseville standards lab cal
and I think another method is used there.

Thanks,

Karl

just for clarification: are you trying to measure the source match of a component used in a leveling or ratio loop (like a splitter) or trying to characterize the source match of the VNA?

To measure the equivalent source match of a two-resistor splitter you must measure the reflection coefficient of the output port of interest, with the other output port terminated and the input port terminated. Your result should be a magnitude of 0.25. Next, you must perform a transmission measurement from the output port of interest to the other output port, maintaining the termination on the input port. The result should be -12dB which converts to 0.25. Subtract your second result from your first result to get your answer for the one output port. Repeat the process in the opposite direction for the other output port. Of course in the real world these won't both be exactly 0.25 and this simplification is omitting the phase component. For the best results you'll want the magnitude and phase of both measurements. In order to subtract one from the other you will have to convert both into real and imaginary values, perform the subtraction, and convert the result back into polar form. See Google for the conversion details. Hope that helped.